Conventionally, a tracked vehicle represented by a construction machine, such as a bulldozer and a hydraulic excavator, is driven by iron crawler belts rotated by power transmitted through drive wheels. The iron crawler belts are supported by the drive wheels, free wheels and upper and lower rollers provided between the drive and free wheels. Recently, rubber crawler belts also have been used instead of iron crawler belts in order to reduce noise and vibrations coming from the crawler belts and wheels. The rubber crawler belts are formed by equidistantly embedding metallic core members in endless rubber belts. The rubber crawler belts are driven by the engagement between the core members and the teeth of the drive wheels.
Generally, an iron crawler belt engages with every other tooth of an odd number of teeth of a drive wheel. Therefore, the teeth which engage with the iron crawler belt shift by one pitch every rotation thereof. In other words, every other tooth comes into engagement during one rotation and the other teeth come in the engagement during the next rotation. Such an every-other-tooth engagement reduces abrasion loss of the teeth of the drive wheel. However, this every-other-tooth engagement results in a large link pitch of the crawler belts in a large vehicle. When such a crawler belt is wound on the drive wheel and the free wheel, a large bending angle results between neighboring links and, thus, the crawler belt forms a polygonal shape. Thus, there is a problem that the impact of the links to the drive and free wheels becomes great and causes substantial noise and vibrations.
Such a problem is also found in a rubber crawler belt. In addition to that, a large bending angle of a rubber crawler belt wound on the drive and free wheels produces a large strain in the lugs provided on the ground contact surface of the rubber crawler belt and may result in a crack in a lug. Thus, durability of the rubber crawler belt decreases.
It has been believed that as in the case of an iron crawler belt, a single tooth of the drive wheel transmits more than a half of the entire driving force to a rubber crawler belt. Therefore, since the rubber and the core members must be adhered firmly, the area of right and left wing portions of a core member is made large to provide sufficient adhesion strength. As a result, the front-rear directional dimension of the wing portions of a core member becomes larger than the interval between the tips of the teeth, and, hence, makes it impossible to arrange core members so as to leave gaps therebetween which enable the teeth of a drive wheel to serially engage with the core members. Inevitably, a rubber crawler belt is formed which has a large double pitch for every-other-tooth engagement. Since such a rubber crawler belt has large gaps between rolling rail surfaces formed on the core members, lower rollers fall into the gaps during travelling of the vehicle and, thus, cause driving vibrations.
A rubber crawler belt of a short pitch may be formed which engages with every tooth of a drive wheel instead of every other tooth. However, there is another requirement that a large ground contact area of the lugs of a rubber crawler belt be provided in order to obtain low lug surface pressure, i.e., to provide sufficient abrasive service life of the lugs. Therefore, if one lug is provided for one core member in such a short pitch rubber crawler belt, freedom with respect to the shape of the lug decreases, and a large sheered area of soil cannot be obtained, resulting in reduced tractive power.
Further, because grooves are formed as bending portions between the core members, lower rollers are not firmly supported by portions between the core members. Therefore, there is a problem that during travelling of the vehicle, the lower rollers fall in between the core members and, hence, inevitably cause vibrations.
When a rubber crawler belt is wound and bent on a drive wheel and a free wheel, grooves formed between the core members are substantially distorted since rigidity of the grooves is low. Therefore, flapping of the crawler belt and bumping noise are likely to result.
Since lugs are separately provided for the individual core members, the lugs clutch into the ground intermittently, thus increasing vibratory force of the crawler belt.
There is a short pitch rubber crawler belt comprising right and left side lugs which substantially cover the projection planes of the right and left wing portions, respectively, of two neighboring core members, and which are shifted by one pitch from each other. However, because gaps between the lugs of both right and left sides exist between core members and the gaps between the lugs of one side are shifted by one pitch from the gaps between the lugs of the other side, rigidity of rubber portions between the core members significantly differs between the right side and the left side. When this rubber crawler belt is wound and bent on a drive wheel and a free wheel, the crawler belt may be twisted and break at a gap. In addition, there is a problem in that the lower roller which has come between core members falls toward the gap between lugs.
The present invention is intended to solve the above problems of the conventional art. It is an object of the present invention to provide a short pitch rubber crawler belt of a tracked vehicle which engages with every tooth of the drive wheel, reduces noise and vibrations caused during travelling of the vehicle, increases rigidity of the crawler belt and tractive power, and reduces the bending strain of the crawler belt and the abrasion of lugs.